I've been looking again at some Google images and I really am still astounded that William could disappear into thin air within a period of five minutes or so.
The aerial view above shows just how close William would have been to the house when he disappeared. Even if he'd managed to get down to the bottom section of Benaroon Drive, he still would have been easily seen in his Spiderman suit IMO. Surely he would have heard his mother and others calling out to him. Why would he just take off and not come back? Did he think he was in trouble? If someone did in fact grab William, wouldn't he have screamed or called out for Mummy? If this was an abduction, it was done very, very quickly and the abductor was gone within minutes, on foot no less. What kind of person would lurk around for an hour or more just to grab a little boy who just happened to be playing in his grandmother's backyard on that particular morning? A little boy who only arrived at his grandmother's place the evening before? Sorry this scenario just doesn't work for me.
Did William hear a car pull up in the driveway, and thinking it was his father, ran around to meet him?
I keep looking at that aerial shot and it gives me chills. Something is very off here.